# orm/mapper.py
# Copyright (C) 2005, 2006, 2007, 2008 Michael Bayer mike_mp@zzzcomputing.com
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Defines the [sqlalchemy.orm.mapper#Mapper] class, the central configurational
unit which associates a class with a database table.

This is a semi-private module; the main configurational API of the ORM is
available in [sqlalchemy.orm#].
"""

import weakref
from itertools import chain
from sqlalchemy import sql, util, exceptions, logging
from sqlalchemy.sql import expression, visitors, operators, util as sqlutil
from sqlalchemy.orm import sync, attributes
from sqlalchemy.orm.interfaces import MapperProperty, EXT_CONTINUE, PropComparator
from sqlalchemy.orm.util import has_identity, _state_has_identity, _is_mapped_class, has_mapper, \
    _state_mapper, class_mapper, object_mapper, _class_to_mapper,\
    ExtensionCarrier, state_str, instance_str
    
__all__ = ['Mapper', 'class_mapper', 'object_mapper', '_mapper_registry']

_mapper_registry = weakref.WeakKeyDictionary()
_new_mappers = False
_already_compiling = False

# a list of MapperExtensions that will be installed in all mappers by default
global_extensions = []

# a constant returned by _get_attr_by_column to indicate
# this mapper is not handling an attribute for a particular
# column
NO_ATTRIBUTE = util.symbol('NO_ATTRIBUTE')

# lock used to synchronize the "mapper compile" step
_COMPILE_MUTEX = util.threading.RLock()

# initialize these lazily
ColumnProperty = None
SynonymProperty = None
ComparableProperty = None
_expire_state = None


class Mapper(object):
    """Define the correlation of class attributes to database table
    columns.

    Instances of this class should be constructed via the
    [sqlalchemy.orm#mapper()] function.
    """

    def __init__(self,
                 class_,
                 local_table,
                 properties = None,
                 primary_key = None,
                 non_primary = False,
                 inherits = None,
                 inherit_condition = None,
                 inherit_foreign_keys = None,
                 extension = None,
                 order_by = False,
                 allow_column_override = False,
                 entity_name = None,
                 always_refresh = False,
                 version_id_col = None,
                 polymorphic_on=None,
                 _polymorphic_map=None,
                 polymorphic_identity=None,
                 polymorphic_fetch=None,
                 concrete=False,
                 select_table=None,
                 with_polymorphic=None,
                 allow_null_pks=False,
                 batch=True,
                 column_prefix=None,
                 include_properties=None,
                 exclude_properties=None,
                 eager_defaults=False):
        """Construct a new mapper.

        Mappers are normally constructed via the [sqlalchemy.orm#mapper()]
        function.  See for details.
        
        """

        self.class_ = class_
        self.entity_name = entity_name
        self.primary_key_argument = primary_key
        self.non_primary = non_primary
        self.order_by = order_by
        self.always_refresh = always_refresh
        self.version_id_col = version_id_col
        self.concrete = concrete
        self.single = False
        self.inherits = inherits
        self.local_table = local_table
        self.inherit_condition = inherit_condition
        self.inherit_foreign_keys = inherit_foreign_keys
        self.extension = extension
        self._init_properties = properties or {}
        self.allow_column_override = allow_column_override
        self.allow_null_pks = allow_null_pks
        self.delete_orphans = []
        self.batch = batch
        self.eager_defaults = eager_defaults
        self.column_prefix = column_prefix
        self.polymorphic_on = polymorphic_on
        self._eager_loaders = util.Set()
        self._dependency_processors = []
        self._clause_adapter = None
        self._requires_row_aliasing = False
        self.__inherits_equated_pairs = None
        
        if not issubclass(class_, object):
            raise exceptions.ArgumentError("Class '%s' is not a new-style class" % class_.__name__)

        self.select_table = select_table
        if select_table:
            if with_polymorphic:
                raise exceptions.ArgumentError("select_table can't be used with with_polymorphic (they define conflicting settings)")
            self.with_polymorphic = ('*', select_table)
        else:
            if with_polymorphic == '*':
                self.with_polymorphic = ('*', None)
            elif isinstance(with_polymorphic, (tuple, list)):
                if isinstance(with_polymorphic[0], (basestring, tuple, list)):
                    self.with_polymorphic = with_polymorphic
                else:
                    self.with_polymorphic = (with_polymorphic, None)
            elif with_polymorphic is not None:
                raise exceptions.ArgumentError("Invalid setting for with_polymorphic")
            else:
                self.with_polymorphic = None
        
        if isinstance(self.local_table, expression._SelectBaseMixin):
            util.warn("mapper %s creating an alias for the given selectable - use Class attributes for queries." % self)
            self.local_table = self.local_table.alias()
        
        if self.with_polymorphic and isinstance(self.with_polymorphic[1], expression._SelectBaseMixin):
            self.with_polymorphic[1] = self.with_polymorphic[1].alias()

        # our 'polymorphic identity', a string name that when located in a result set row
        # indicates this Mapper should be used to construct the object instance for that row.
        self.polymorphic_identity = polymorphic_identity

        if polymorphic_fetch not in (None, 'union', 'select', 'deferred'):
            raise exceptions.ArgumentError("Invalid option for 'polymorphic_fetch': '%s'" % polymorphic_fetch)
        if polymorphic_fetch is None:
            self.polymorphic_fetch = (self.with_polymorphic is None) and 'select' or 'union'
        else:
            self.polymorphic_fetch = polymorphic_fetch

        # a dictionary of 'polymorphic identity' names, associating those names with
        # Mappers that will be used to construct object instances upon a select operation.
        if _polymorphic_map is None:
            self.polymorphic_map = {}
        else:
            self.polymorphic_map = _polymorphic_map

        self.columns = self.c = util.OrderedProperties()

        self.include_properties = include_properties
        self.exclude_properties = exclude_properties

        # a set of all mappers which inherit from this one.
        self._inheriting_mappers = util.Set()

        self.__props_init = False

        self.__should_log_info = logging.is_info_enabled(self.logger)
        self.__should_log_debug = logging.is_debug_enabled(self.logger)

        self.__compile_class()
        self.__compile_inheritance()
        self.__compile_extensions()
        self.__compile_properties()
        self.__compile_pks()
        global _new_mappers
        _new_mappers = True
        self.__log("constructed")

    def __log(self, msg):
        if self.__should_log_info:
            self.logger.info("(" + self.class_.__name__ + "|" + (self.entity_name is not None and "/%s" % self.entity_name or "") + (self.local_table and self.local_table.description or str(self.local_table)) + (self.non_primary and "|non-primary" or "") + ") " + msg)

    def __log_debug(self, msg):
        if self.__should_log_debug:
            self.logger.debug("(" + self.class_.__name__ + "|" + (self.entity_name is not None and "/%s" % self.entity_name or "") + (self.local_table and self.local_table.description or str(self.local_table)) + (self.non_primary and "|non-primary" or "") + ") " + msg)

    def _is_orphan(self, obj):
        o = False
        for mapper in self.iterate_to_root():
            for (key,klass) in mapper.delete_orphans:
                if attributes.has_parent(klass, obj, key, optimistic=has_identity(obj)):
                    return False
            o = o or bool(mapper.delete_orphans)
        return o

    def get_property(self, key, resolve_synonyms=False, raiseerr=True):
        """return a MapperProperty associated with the given key."""

        self.compile()
        return self._get_property(key, resolve_synonyms=resolve_synonyms, raiseerr=raiseerr)

    def _get_property(self, key, resolve_synonyms=False, raiseerr=True):
        """private in-compilation version of get_property()."""

        prop = self.__props.get(key, None)
        if resolve_synonyms:
            while isinstance(prop, SynonymProperty):
                prop = self.__props.get(prop.name, None)
        if prop is None and raiseerr:
            raise exceptions.InvalidRequestError("Mapper '%s' has no property '%s'" % (str(self), key))
        return prop

    def iterate_properties(self):
        self.compile()
        return self.__props.itervalues()
    iterate_properties = property(iterate_properties, doc="returns an iterator of all MapperProperty objects.")

    def __adjust_wp_selectable(self, spec=None, selectable=False):
        """given a with_polymorphic() argument, resolve it against this mapper's with_polymorphic setting"""
        
        isdefault = False
        if self.with_polymorphic:
            isdefault = not spec and selectable is False

            if not spec:
                spec = self.with_polymorphic[0]
            if selectable is False:
                selectable = self.with_polymorphic[1]
                
        return spec, selectable, isdefault
        
    def __mappers_from_spec(self, spec, selectable):
        """given a with_polymorphic() argument, return the set of mappers it represents.
        
        Trims the list of mappers to just those represented within the given selectable, if present.
        This helps some more legacy-ish mappings.
        
        """
        if spec == '*':
            mappers = list(self.polymorphic_iterator())
        elif spec:
            mappers = [_class_to_mapper(m) for m in util.to_list(spec)]
        else:
            mappers = []
        
        if selectable:
            tables = util.Set(sqlutil.find_tables(selectable))
            mappers = [m for m in mappers if m.local_table in tables]
            
        return mappers
    __mappers_from_spec = util.conditional_cache_decorator(__mappers_from_spec)
    
    def __selectable_from_mappers(self, mappers):
        """given a list of mappers (assumed to be within this mapper's inheritance hierarchy),
        construct an outerjoin amongst those mapper's mapped tables.
        
        """
        from_obj = self.mapped_table
        for m in mappers:
            if m is self:
                continue
            if m.concrete:
                raise exceptions.InvalidRequestError("'with_polymorphic()' requires 'selectable' argument when concrete-inheriting mappers are used.")
            elif not m.single:
                from_obj = from_obj.outerjoin(m.local_table, m.inherit_condition)
        
        return from_obj
    __selectable_from_mappers = util.conditional_cache_decorator(__selectable_from_mappers)
    
    def _with_polymorphic_mappers(self, spec=None, selectable=False):
        spec, selectable, isdefault = self.__adjust_wp_selectable(spec, selectable)
        return self.__mappers_from_spec(spec, selectable, cache=isdefault)
        
    def _with_polymorphic_selectable(self, spec=None, selectable=False):
        spec, selectable, isdefault = self.__adjust_wp_selectable(spec, selectable)
        if selectable:
            return selectable
        else:
            return self.__selectable_from_mappers(self.__mappers_from_spec(spec, selectable, cache=isdefault), cache=isdefault)
    
    def _with_polymorphic_args(self, spec=None, selectable=False):
        spec, selectable, isdefault = self.__adjust_wp_selectable(spec, selectable)
        mappers = self.__mappers_from_spec(spec, selectable, cache=isdefault)
        if selectable:
            return mappers, selectable
        else:
            return mappers, self.__selectable_from_mappers(mappers, cache=isdefault)
        
    def _iterate_polymorphic_properties(self, spec=None, selectable=False):
        return iter(util.OrderedSet(
            chain(*[list(mapper.iterate_properties) for mapper in [self] + self._with_polymorphic_mappers(spec, selectable)])
        ))

    def properties(self):
        raise NotImplementedError("Public collection of MapperProperty objects is provided by the get_property() and iterate_properties accessors.")
    properties = property(properties)

    def compiled(self):
        """return True if this mapper is compiled"""
        return self.__props_init
    compiled = property(compiled)

    def dispose(self):
        # disaable any attribute-based compilation
        self.__props_init = True
        try:
            del self.class_.c
        except AttributeError:
            pass
        if not self.non_primary and self.entity_name in self._class_state.mappers:
            del self._class_state.mappers[self.entity_name]
        if not self._class_state.mappers:
            attributes.unregister_class(self.class_)

    def compile(self):
        """Compile this mapper and all other non-compiled mappers.
        
        This method checks the local compiled status as well as for
        any new mappers that have been defined, and is safe to call 
        repeatedly.
        """
        
        global _new_mappers
        if self.__props_init and not _new_mappers:
            return self
            
        _COMPILE_MUTEX.acquire()
        global _already_compiling
        if _already_compiling:
            self.__initialize_properties()
            return
        _already_compiling = True
        try:

            # double-check inside mutex
            if self.__props_init and not _new_mappers:
                return self

            # initialize properties on all mappers
            for mapper in list(_mapper_registry):
                if not mapper.__props_init:
                    mapper.__initialize_properties()

            _new_mappers = False
            return self
        finally:
            _already_compiling = False
            _COMPILE_MUTEX.release()

    def __initialize_properties(self):
        """Call the ``init()`` method on all ``MapperProperties``
        attached to this mapper.
        
        This is a deferred configuration step which is intended
        to execute once all mappers have been constructed.
        """

        self.__log("__initialize_properties() started")
        l = [(key, prop) for key, prop in self.__props.iteritems()]
        for key, prop in l:
            self.__log("initialize prop " + key)
            if getattr(prop, 'key', None) is None:
                prop.init(key, self)
        self.__log("__initialize_properties() complete")
        self.__props_init = True


    def __compile_extensions(self):
        """Go through the global_extensions list as well as the list
        of ``MapperExtensions`` specified for this ``Mapper`` and
        creates a linked list of those extensions.
        """

        extlist = util.OrderedSet()

        extension = self.extension
        if extension:
            for ext_obj in util.to_list(extension):
                # local MapperExtensions have already instrumented the class
                extlist.add(ext_obj)

        if self.inherits:
            for ext in self.inherits.extension:
                if ext not in extlist:
                    extlist.add(ext)
                    ext.instrument_class(self, self.class_)
        else:
            for ext in global_extensions:
                if isinstance(ext, type):
                    ext = ext()
                if ext not in extlist:
                    extlist.add(ext)
                    ext.instrument_class(self, self.class_)

        self.extension = ExtensionCarrier()
        for ext in extlist:
            self.extension.append(ext)

    def __compile_inheritance(self):
        """Configure settings related to inherting and/or inherited mappers being present."""

        if self.inherits:
            if isinstance(self.inherits, type):
                self.inherits = class_mapper(self.inherits, compile=False)
            else:
                self.inherits = self.inherits
            if not issubclass(self.class_, self.inherits.class_):
                raise exceptions.ArgumentError("Class '%s' does not inherit from '%s'" % (self.class_.__name__, self.inherits.class_.__name__))
            if self.non_primary != self.inherits.non_primary:
                np = not self.non_primary and "primary" or "non-primary"
                raise exceptions.ArgumentError("Inheritance of %s mapper for class '%s' is only allowed from a %s mapper" % (np, self.class_.__name__, np))
            # inherit_condition is optional.
            if self.local_table is None:
                self.local_table = self.inherits.local_table
                self.mapped_table = self.inherits.mapped_table
                self.single = True
            elif not self.local_table is self.inherits.local_table:
                if self.concrete:
                    self.mapped_table = self.local_table
                    for mapper in self.iterate_to_root():
                        if mapper.polymorphic_on:
                            mapper._requires_row_aliasing = True
                else:
                    if self.inherit_condition is None:
                        # figure out inherit condition from our table to the immediate table
                        # of the inherited mapper, not its full table which could pull in other
                        # stuff we dont want (allows test/inheritance.InheritTest4 to pass)
                        self.inherit_condition = sqlutil.join_condition(self.inherits.local_table, self.local_table)
                    self.mapped_table = sql.join(self.inherits.mapped_table, self.local_table, self.inherit_condition)
                    
                    fks = util.to_set(self.inherit_foreign_keys)
                    self.__inherits_equated_pairs = sqlutil.criterion_as_pairs(self.mapped_table.onclause, consider_as_foreign_keys=fks)
            else:
                self.mapped_table = self.local_table
            if self.polymorphic_identity is not None:
                self.inherits.polymorphic_map[self.polymorphic_identity] = self
                if self.polymorphic_on is None:
                    for mapper in self.iterate_to_root():
                        # try to set up polymorphic on using correesponding_column(); else leave
                        # as None
                        if mapper.polymorphic_on:
                            self.polymorphic_on = self.mapped_table.corresponding_column(mapper.polymorphic_on)
                            break
                    else:
                        # TODO: this exception not covered
                        raise exceptions.ArgumentError("Mapper '%s' specifies a polymorphic_identity of '%s', but no mapper in it's hierarchy specifies the 'polymorphic_on' column argument" % (str(self), self.polymorphic_identity))

            if self.polymorphic_identity and not self.concrete:
                self._identity_class = self.inherits._identity_class
            else:
                self._identity_class = self.class_

            if self.version_id_col is None:
                self.version_id_col = self.inherits.version_id_col

            for mapper in self.iterate_to_root():
                util.reset_cached(mapper, '_equivalent_columns')

            if self.order_by is False:
                self.order_by = self.inherits.order_by
            self.polymorphic_map = self.inherits.polymorphic_map
            self.batch = self.inherits.batch
            self.inherits._inheriting_mappers.add(self)
            self.base_mapper = self.inherits.base_mapper
            self._all_tables = self.inherits._all_tables
        else:
            self._all_tables = util.Set()
            self.base_mapper = self
            self.mapped_table = self.local_table
            if self.polymorphic_identity:
                if self.polymorphic_on is None:
                    raise exceptions.ArgumentError("Mapper '%s' specifies a polymorphic_identity of '%s', but no mapper in it's hierarchy specifies the 'polymorphic_on' column argument" % (str(self), self.polymorphic_identity))
                self.polymorphic_map[self.polymorphic_identity] = self
            self._identity_class = self.class_
        
        if self.mapped_table is None:
            raise exceptions.ArgumentError("Mapper '%s' does not have a mapped_table specified.  (Are you using the return value of table.create()?  It no longer has a return value.)" % str(self))

    def __compile_pks(self):

        self.tables = sqlutil.find_tables(self.mapped_table)

        if not self.tables:
            raise exceptions.InvalidRequestError("Could not find any Table objects in mapped table '%s'" % str(self.mapped_table))

        self._pks_by_table = {}
        self._cols_by_table = {}

        all_cols = util.Set(chain(*[col.proxy_set for col in self._columntoproperty]))
        pk_cols = util.Set([c for c in all_cols if c.primary_key])

        # identify primary key columns which are also mapped by this mapper.
        for t in util.Set(self.tables + [self.mapped_table]):
            self._all_tables.add(t)
            if t.primary_key and pk_cols.issuperset(t.primary_key):
                # ordering is important since it determines the ordering of mapper.primary_key (and therefore query.get())
                self._pks_by_table[t] = util.OrderedSet(t.primary_key).intersection(pk_cols)
            self._cols_by_table[t] = util.OrderedSet(t.c).intersection(all_cols)

        # if explicit PK argument sent, add those columns to the primary key mappings
        if self.primary_key_argument:
            for k in self.primary_key_argument:
                if k.table not in self._pks_by_table:
                    self._pks_by_table[k.table] = util.OrderedSet()
                self._pks_by_table[k.table].add(k)

        if self.mapped_table not in self._pks_by_table or len(self._pks_by_table[self.mapped_table]) == 0:
            raise exceptions.ArgumentError("Mapper %s could not assemble any primary key columns for mapped table '%s'" % (self, self.mapped_table.description))

        if self.inherits and not self.concrete and not self.primary_key_argument:
            # if inheriting, the "primary key" for this mapper is that of the inheriting (unless concrete or explicit)
            self.primary_key = self.inherits.primary_key
        else:
            # determine primary key from argument or mapped_table pks - reduce to the minimal set of columns
            if self.primary_key_argument:
                primary_key = sqlutil.reduce_columns([self.mapped_table.corresponding_column(c) for c in self.primary_key_argument])
            else:
                primary_key = sqlutil.reduce_columns(self._pks_by_table[self.mapped_table])

            if len(primary_key) == 0:
                raise exceptions.ArgumentError("Mapper %s could not assemble any primary key columns for mapped table '%s'" % (self, self.mapped_table.description))

            self.primary_key = primary_key
            self.__log("Identified primary key columns: " + str(primary_key))

    def _get_clause(self):
        """create a "get clause" based on the primary key.  this is used
        by query.get() and many-to-one lazyloads to load this item
        by primary key.
        
        """
        params = [(primary_key, sql.bindparam(None, type_=primary_key.type)) for primary_key in self.primary_key]
        return sql.and_(*[k==v for (k, v) in params]), dict(params)
    _get_clause = property(util.cache_decorator(_get_clause))
    
    def _equivalent_columns(self):
        """Create a map of all *equivalent* columns, based on
        the determination of column pairs that are equated to
        one another either by an established foreign key relationship
        or by a joined-table inheritance join.

        This is used to determine the minimal set of primary key
        columns for the mapper, as well as when relating
        columns to those of a polymorphic selectable (i.e. a UNION of
        several mapped tables), as that selectable usually only contains
        one column in its columns clause out of a group of several which
        are equated to each other.

        The resulting structure is a dictionary of columns mapped
        to lists of equivalent columns, i.e.

        {
            tablea.col1:
                set([tableb.col1, tablec.col1]),
            tablea.col2:
                set([tabled.col2])
        }

        """

        result = {}
        def visit_binary(binary):
            if binary.operator == operators.eq:
                if binary.left in result:
                    result[binary.left].add(binary.right)
                else:
                    result[binary.left] = util.Set([binary.right])
                if binary.right in result:
                    result[binary.right].add(binary.left)
                else:
                    result[binary.right] = util.Set([binary.left])
        for mapper in self.base_mapper.polymorphic_iterator():
            if mapper.inherit_condition:
                visitors.traverse(mapper.inherit_condition, visit_binary=visit_binary)

        # TODO: matching of cols to foreign keys might better be generalized
        # into general column translation (i.e. corresponding_column)

        # recursively descend into the foreign key collection of the given column
        # and assemble each FK-related col as an "equivalent" for the given column
        def equivs(col, recursive, equiv):
            if col in recursive:
                return
            recursive.add(col)
            for fk in col.foreign_keys:
                if fk.column not in result:
                    result[fk.column] = util.Set()
                result[fk.column].add(equiv)
                equivs(fk.column, recursive, col)

        for column in (self.primary_key_argument or self._pks_by_table[self.mapped_table]):
            for col in column.proxy_set:
                if not col.foreign_keys:
                    if col not in result:
                        result[col] = util.Set()
                    result[col].add(col)
                else:
                    equivs(col, util.Set(), col)

        return result
    _equivalent_columns = property(util.cache_decorator(_equivalent_columns))

    class _CompileOnAttr(PropComparator):
        """A placeholder descriptor which triggers compilation on access."""

        def __init__(self, class_, key):
            self.class_ = class_
            self.key = key
            self.existing_prop = getattr(class_, key, None)

        def __getattribute__(self, key):
            cls = object.__getattribute__(self, 'class_')
            clskey = object.__getattribute__(self, 'key')

            if key.startswith('__'):
                return object.__getattribute__(self, key)

            class_mapper(cls)

            if cls.__dict__.get(clskey) is self:
                # FIXME: there should not be any scenarios where
                # a mapper compile leaves this CompileOnAttr in
                # place.
                util.warn(
                    ("Attribute '%s' on class '%s' was not replaced during "
                     "mapper compilation operation") % (clskey, cls.__name__))
                # clean us up explicitly
                delattr(cls, clskey)

            return getattr(getattr(cls, clskey), key)

    def __compile_properties(self):

        # object attribute names mapped to MapperProperty objects
        self.__props = util.OrderedDict()

        # table columns mapped to lists of MapperProperty objects
        # using a list allows a single column to be defined as
        # populating multiple object attributes
        self._columntoproperty = {}

        # load custom properties
        if self._init_properties:
            for key, prop in self._init_properties.iteritems():
                self._compile_property(key, prop, False)

        # pull properties from the inherited mapper if any.
        if self.inherits:
            for key, prop in self.inherits.__props.iteritems():
                if key not in self.__props:
                    self._adapt_inherited_property(key, prop)

        # create properties for each column in the mapped table,
        # for those columns which don't already map to a property
        for column in self.mapped_table.columns:
            if column in self._columntoproperty:
                continue

            if (self.include_properties is not None and
                column.key not in self.include_properties):
                self.__log("not including property %s" % (column.key))
                continue

            if (self.exclude_properties is not None and
                column.key in self.exclude_properties):
                self.__log("excluding property %s" % (column.key))
                continue

            column_key = (self.column_prefix or '') + column.key

            self._compile_property(column_key, column, init=False, setparent=True)
        
        # do a special check for the "discriminiator" column, as it may only be present
        # in the 'with_polymorphic' selectable but we need it for the base mapper
        if self.polymorphic_on and self.polymorphic_on not in self._columntoproperty: 
           col = self.mapped_table.corresponding_column(self.polymorphic_on) or self.polymorphic_on
           self._compile_property(col.key, ColumnProperty(col), init=False, setparent=True)
            
    def _adapt_inherited_property(self, key, prop):
        if not self.concrete:
            self._compile_property(key, prop, init=False, setparent=False)
        # TODO: concrete properties dont adapt at all right now....will require copies of relations() etc.

    def _compile_property(self, key, prop, init=True, setparent=True):
        self.__log("_compile_property(%s, %s)" % (key, prop.__class__.__name__))

        if not isinstance(prop, MapperProperty):
            # we were passed a Column or a list of Columns; generate a ColumnProperty
            columns = util.to_list(prop)
            column = columns[0]
            if not expression.is_column(column):
                raise exceptions.ArgumentError("%s=%r is not an instance of MapperProperty or Column" % (key, prop))

            prop = self.__props.get(key, None)

            if isinstance(prop, ColumnProperty):
                # TODO: the "property already exists" case is still not well defined here.
                # assuming single-column, etc.

                if prop.parent is not self:
                    # existing ColumnProperty from an inheriting mapper.
                    # make a copy and append our column to it
                    prop = prop.copy()
                prop.columns.append(column)
                self.__log("appending to existing ColumnProperty %s" % (key))
            elif prop is None:
                mapped_column = []
                for c in columns:
                    mc = self.mapped_table.corresponding_column(c)
                    if not mc:
                        raise exceptions.ArgumentError("Column '%s' is not represented in mapper's table.  Use the `column_property()` function to force this column to be mapped as a read-only attribute." % str(c))
                    mapped_column.append(mc)
                prop = ColumnProperty(*mapped_column)
            else:
                if not self.allow_column_override:
                    raise exceptions.ArgumentError("WARNING: column '%s' not being added due to property '%s'.  Specify 'allow_column_override=True' to mapper() to ignore this condition." % (column.key, repr(prop)))
                else:
                    return

        if isinstance(prop, ColumnProperty):
            col = self.mapped_table.corresponding_column(prop.columns[0])
            # col might not be present! the selectable given to the mapper need not include "deferred"
            # columns (included in zblog tests)
            if col is None:
                col = prop.columns[0]
            else:
                # if column is coming in after _cols_by_table was initialized, ensure the col is in the 
                # right set
                if hasattr(self, '_cols_by_table') and col.table in self._cols_by_table and col not in self._cols_by_table[col.table]:
                    self._cols_by_table[col.table].add(col)

            self.columns[key] = col
            for col in prop.columns:
                for col in col.proxy_set:
                    self._columntoproperty[col] = prop
            
                
        elif isinstance(prop, SynonymProperty) and setparent:
            if prop.descriptor is None:
                prop.descriptor = getattr(self.class_, key, None)
                if isinstance(prop.descriptor, Mapper._CompileOnAttr):
                    prop.descriptor = object.__getattribute__(prop.descriptor, 'existing_prop')
            if prop.map_column:
                if not key in self.mapped_table.c:
                    raise exceptions.ArgumentError("Can't compile synonym '%s': no column on table '%s' named '%s'"  % (prop.name, self.mapped_table.description, key))
                self._compile_property(prop.name, ColumnProperty(self.mapped_table.c[key]), init=init, setparent=setparent)
        elif isinstance(prop, ComparableProperty) and setparent:
            # refactor me
            if prop.descriptor is None:
                prop.descriptor = getattr(self.class_, key, None)
                if isinstance(prop.descriptor, Mapper._CompileOnAttr):
                    prop.descriptor = object.__getattribute__(prop.descriptor,
                                                              'existing_prop')
        self.__props[key] = prop

        if setparent:
            prop.set_parent(self)

            if not self.non_primary:
                setattr(self.class_, key, Mapper._CompileOnAttr(self.class_, key))

        if init:
            prop.init(key, self)
        
        for mapper in self._inheriting_mappers:
            mapper._adapt_inherited_property(key, prop)

    def __compile_class(self):
        """If this mapper is to be a primary mapper (i.e. the
        non_primary flag is not set), associate this Mapper with the
        given class_ and entity name.

        Subsequent calls to ``class_mapper()`` for the class_/entity
        name combination will return this mapper.  Also decorate the
        `__init__` method on the mapped class to include optional
        auto-session attachment logic.
        """

        if self.non_primary:
            if not hasattr(self.class_, '_class_state'):
                raise exceptions.InvalidRequestError("Class %s has no primary mapper configured.  Configure a primary mapper first before setting up a non primary Mapper.")
            self._class_state = self.class_._class_state
            _mapper_registry[self] = True
            return

        if not self.non_primary and '_class_state' in self.class_.__dict__ and (self.entity_name in self.class_._class_state.mappers):
             raise exceptions.ArgumentError("Class '%s' already has a primary mapper defined with entity name '%s'.  Use non_primary=True to create a non primary Mapper.  clear_mappers() will remove *all* current mappers from all classes." % (self.class_, self.entity_name))

        def extra_init(class_, oldinit, instance, args, kwargs):
            self.compile()
            if 'init_instance' in self.extension.methods:
                self.extension.init_instance(self, class_, oldinit, instance, args, kwargs)

        def on_exception(class_, oldinit, instance, args, kwargs):
            util.warn_exception(self.extension.init_failed, self, class_, oldinit, instance, args, kwargs)

        attributes.register_class(self.class_, extra_init=extra_init, on_exception=on_exception, deferred_scalar_loader=_load_scalar_attributes)

        self._class_state = self.class_._class_state
        _mapper_registry[self] = True

        self.class_._class_state.mappers[self.entity_name] = self

        for ext in util.to_list(self.extension, []):
            ext.instrument_class(self, self.class_)

        if self.entity_name is None:
            self.class_.c = self.c

    def common_parent(self, other):
        """Return true if the given mapper shares a common inherited parent as this mapper."""

        return self.base_mapper is other.base_mapper

    def isa(self, other):
        """Return True if the given mapper inherits from this mapper."""

        m = other
        while m is not self and m.inherits:
            m = m.inherits
        return m is self

    def iterate_to_root(self):
        m = self
        while m:
            yield m
            m = m.inherits

    def polymorphic_iterator(self):
        """Iterate through the collection including this mapper and
        all descendant mappers.

        This includes not just the immediately inheriting mappers but
        all their inheriting mappers as well.

        To iterate through an entire hierarchy, use
        ``mapper.base_mapper.polymorphic_iterator()``."""

        yield self
        for mapper in self._inheriting_mappers:
            for m in mapper.polymorphic_iterator():
                yield m


    def add_properties(self, dict_of_properties):
        """Add the given dictionary of properties to this mapper,
        using `add_property`.
        """

        for key, value in dict_of_properties.iteritems():
            self.add_property(key, value)

    def add_property(self, key, prop):
        """Add an individual MapperProperty to this mapper.

        If the mapper has not been compiled yet, just adds the
        property to the initial properties dictionary sent to the
        constructor.  If this Mapper has already been compiled, then
        the given MapperProperty is compiled immediately.
        """

        self._init_properties[key] = prop
        self._compile_property(key, prop, init=self.__props_init)

    def __str__(self):
        return "Mapper|" + self.class_.__name__ + "|" + (self.entity_name is not None and "/%s" % self.entity_name or "") + (self.local_table and self.local_table.description or str(self.local_table)) + (self.non_primary and "|non-primary" or "")

    def primary_mapper(self):
        """Return the primary mapper corresponding to this mapper's class key (class + entity_name)."""
        return self._class_state.mappers[self.entity_name]

    def get_session(self):
        """Return the contextual session provided by the mapper
        extension chain, if any.

        Raise ``InvalidRequestError`` if a session cannot be retrieved
        from the extension chain.
        """

        if 'get_session' in self.extension.methods:
            s = self.extension.get_session()
            if s is not EXT_CONTINUE:
                return s

        raise exceptions.InvalidRequestError("No contextual Session is established.")

    def instances(self, cursor, session, *mappers, **kwargs):
        """Return a list of mapped instances corresponding to the rows
        in a given ResultProxy.

        DEPRECATED.
        """

        import sqlalchemy.orm.query
        return sqlalchemy.orm.Query(self, session).instances(cursor, *mappers, **kwargs)
    instances = util.deprecated(None, False)(instances)

    def identity_key_from_row(self, row):
        """Return an identity-map key for use in storing/retrieving an
        item from the identity map.

        row
          A ``sqlalchemy.engine.base.RowProxy`` instance or a
          dictionary corresponding result-set ``ColumnElement``
          instances to their values within a row.
        """
        return (self._identity_class, tuple([row[column] for column in self.primary_key]), self.entity_name)

    def identity_key_from_primary_key(self, primary_key):
        """Return an identity-map key for use in storing/retrieving an
        item from an identity map.

        primary_key
          A list of values indicating the identifier.
        """
        return (self._identity_class, tuple(util.to_list(primary_key)), self.entity_name)

    def identity_key_from_instance(self, instance):
        """Return the identity key for the given instance, based on
        its primary key attributes.

        This value is typically also found on the instance itself
        under the attribute name `_instance_key`.
        """
        return self.identity_key_from_primary_key(self.primary_key_from_instance(instance))

    def _identity_key_from_state(self, state):
        return self.identity_key_from_primary_key(self._primary_key_from_state(state))

    def primary_key_from_instance(self, instance):
        """Return the list of primary key values for the given
        instance.
        """

        return [self._get_state_attr_by_column(instance._state, column) for column in self.primary_key]

    def _primary_key_from_state(self, state):
        return [self._get_state_attr_by_column(state, column) for column in self.primary_key]

    def _canload(self, state, allow_subtypes):
        if self.polymorphic_on or allow_subtypes:
            return self.isa(_state_mapper(state))
        else:
            return state.class_ is self.class_

    def _get_col_to_prop(self, column):
        try:
            return self._columntoproperty[column]
        except KeyError:
            prop = self.__props.get(column.key, None)
            if prop:
                raise exceptions.UnmappedColumnError("Column '%s.%s' is not available, due to conflicting property '%s':%s" % (column.table.name, column.name, column.key, repr(prop)))
            else:
                raise exceptions.UnmappedColumnError("No column %s.%s is configured on mapper %s..." % (column.table.name, column.name, str(self)))

    def _get_state_attr_by_column(self, state, column):
        return self._get_col_to_prop(column).getattr(state, column)

    def _set_state_attr_by_column(self, state, column, value):
        return self._get_col_to_prop(column).setattr(state, value, column)

    def _get_attr_by_column(self, obj, column):
        return self._get_col_to_prop(column).getattr(obj._state, column)

    def _get_committed_attr_by_column(self, obj, column):
        return self._get_col_to_prop(column).getcommitted(obj._state, column)

    def _set_attr_by_column(self, obj, column, value):
        self._get_col_to_prop(column).setattr(obj._state, column, value)

    def _save_obj(self, states, uowtransaction, postupdate=False, post_update_cols=None, single=False):
        """Issue ``INSERT`` and/or ``UPDATE`` statements for a list of objects.

        This is called within the context of a UOWTransaction during a
        flush operation.

        `_save_obj` issues SQL statements not just for instances mapped
        directly by this mapper, but for instances mapped by all
        inheriting mappers as well.  This is to maintain proper insert
        ordering among a polymorphic chain of instances. Therefore
        _save_obj is typically called only on a *base mapper*, or a
        mapper which does not inherit from any other mapper.
        """

        if self.__should_log_debug:
            self.__log_debug("_save_obj() start, " + (single and "non-batched" or "batched"))

        # if batch=false, call _save_obj separately for each object
        if not single and not self.batch:
            for state in states:
                self._save_obj([state], uowtransaction, postupdate=postupdate, post_update_cols=post_update_cols, single=True)
            return

        # if session has a connection callable,
        # organize individual states with the connection to use for insert/update
        if 'connection_callable' in uowtransaction.mapper_flush_opts:
            connection_callable = uowtransaction.mapper_flush_opts['connection_callable']
            tups = [(state, connection_callable(self, state.obj()), _state_has_identity(state)) for state in states]
        else:
            connection = uowtransaction.transaction.connection(self)
            tups = [(state, connection, _state_has_identity(state)) for state in states]

        if not postupdate:
            # call before_XXX extensions
            for state, connection, has_identity in tups:
                mapper = _state_mapper(state)
                if not has_identity:
                    if 'before_insert' in mapper.extension.methods:
                        mapper.extension.before_insert(mapper, connection, state.obj())
                else:
                    if 'before_update' in mapper.extension.methods:
                        mapper.extension.before_update(mapper, connection, state.obj())

        for state, connection, has_identity in tups:
            # detect if we have a "pending" instance (i.e. has no instance_key attached to it),
            # and another instance with the same identity key already exists as persistent.  convert to an
            # UPDATE if so.
            mapper = _state_mapper(state)
            instance_key = mapper._identity_key_from_state(state)
            if not postupdate and not has_identity and instance_key in uowtransaction.uow.identity_map:
                existing = uowtransaction.uow.identity_map[instance_key]._state
                if not uowtransaction.is_deleted(existing):
                    raise exceptions.FlushError("New instance %s with identity key %s conflicts with persistent instance %s" % (state_str(state), str(instance_key), state_str(existing)))
                if self.__should_log_debug:
                    self.__log_debug("detected row switch for identity %s.  will update %s, remove %s from transaction" % (instance_key, state_str(state), state_str(existing)))
                uowtransaction.set_row_switch(existing)

        inserted_objects = util.Set()
        updated_objects = util.Set()

        table_to_mapper = {}
        for mapper in self.base_mapper.polymorphic_iterator():
            for t in mapper.tables:
                table_to_mapper[t] = mapper

        for table in sqlutil.sort_tables(table_to_mapper.keys()):
            insert = []
            update = []

            for state, connection, has_identity in tups:
                mapper = _state_mapper(state)
                if table not in mapper._pks_by_table:
                    continue
                pks = mapper._pks_by_table[table]
                instance_key = mapper._identity_key_from_state(state)

                if self.__should_log_debug:
                    self.__log_debug("_save_obj() table '%s' instance %s identity %s" % (table.name, state_str(state), str(instance_key)))

                isinsert = not instance_key in uowtransaction.uow.identity_map and not postupdate and not has_identity
                params = {}
                value_params = {}
                hasdata = False

                if isinsert:
                    for col in mapper._cols_by_table[table]:
                        if col is mapper.version_id_col:
                            params[col.key] = 1
                        elif col in pks:
                            value = mapper._get_state_attr_by_column(state, col)
                            if value is not None:
                                params[col.key] = value
                        elif mapper.polymorphic_on and mapper.polymorphic_on.shares_lineage(col):
                            if self.__should_log_debug:
                                self.__log_debug("Using polymorphic identity '%s' for insert column '%s'" % (mapper.polymorphic_identity, col.key))
                            value = mapper.polymorphic_identity
                            if col.default is None or value is not None:
                                params[col.key] = value
                        else:
                            value = mapper._get_state_attr_by_column(state, col)
                            if col.default is None or value is not None:
                                if isinstance(value, sql.ClauseElement):
                                    value_params[col] = value
                                else:
                                    params[col.key] = value
                    insert.append((state, params, mapper, connection, value_params))
                else:
                    for col in mapper._cols_by_table[table]:
                        if col is mapper.version_id_col:
                            params[col._label] = mapper._get_state_attr_by_column(state, col)
                            params[col.key] = params[col._label] + 1
                            for prop in mapper._columntoproperty.values():
                                (added, unchanged, deleted) = attributes.get_history(state, prop.key, passive=True)
                                if added:
                                    hasdata = True
                        elif mapper.polymorphic_on and mapper.polymorphic_on.shares_lineage(col):
                            pass
                        else:
                            if post_update_cols is not None and col not in post_update_cols:
                                if col in pks:
                                    params[col._label] = mapper._get_state_attr_by_column(state, col)
                                continue

                            prop = mapper._columntoproperty[col]
                            (added, unchanged, deleted) = attributes.get_history(state, prop.key, passive=True)
                            if added:
                                if isinstance(added[0], sql.ClauseElement):
                                    value_params[col] = added[0]
                                else:
                                    params[col.key] = prop.get_col_value(col, added[0])
                                if col in pks:
                                    if deleted:
                                        params[col._label] = deleted[0]
                                    else:
                                        # row switch logic can reach us here
                                        params[col._label] = added[0]
                                hasdata = True
                            elif col in pks:
                                params[col._label] = mapper._get_state_attr_by_column(state, col)
                    if hasdata:
                        update.append((state, params, mapper, connection, value_params))

            if update:
                mapper = table_to_mapper[table]
                clause = sql.and_()

                for col in mapper._pks_by_table[table]:
                    clause.clauses.append(col == sql.bindparam(col._label, type_=col.type))

                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    clause.clauses.append(mapper.version_id_col == sql.bindparam(mapper.version_id_col._label, type_=col.type))

                statement = table.update(clause)
                pks = mapper._pks_by_table[table]
                def comparator(a, b):
                    for col in pks:
                        x = cmp(a[1][col._label],b[1][col._label])
                        if x != 0:
                            return x
                    return 0
                update.sort(comparator)

                rows = 0
                for rec in update:
                    (state, params, mapper, connection, value_params) = rec
                    c = connection.execute(statement.values(value_params), params)
                    mapper.__postfetch(uowtransaction, connection, table, state, c, c.last_updated_params(), value_params)

                    # testlib.pragma exempt:__hash__
                    updated_objects.add((state, connection))
                    rows += c.rowcount

                if c.supports_sane_rowcount() and rows != len(update):
                    raise exceptions.ConcurrentModificationError("Updated rowcount %d does not match number of objects updated %d" % (rows, len(update)))

            if insert:
                statement = table.insert()
                def comparator(a, b):
                    return cmp(a[0].insert_order, b[0].insert_order)
                insert.sort(comparator)
                for rec in insert:
                    (state, params, mapper, connection, value_params) = rec
                    c = connection.execute(statement.values(value_params), params)
                    primary_key = c.last_inserted_ids()

                    if primary_key is not None:
                        # set primary key attributes
                        for i, col in enumerate(mapper._pks_by_table[table]):
                            if mapper._get_state_attr_by_column(state, col) is None and len(primary_key) > i:
                                mapper._set_state_attr_by_column(state, col, primary_key[i])
                    mapper.__postfetch(uowtransaction, connection, table, state, c, c.last_inserted_params(), value_params)

                    # synchronize newly inserted ids from one table to the next
                    # TODO: this fires off more than needed, try to organize syncrules
                    # per table
                    for m in util.reversed(list(mapper.iterate_to_root())):
                        if m.__inherits_equated_pairs:
                            m.__synchronize_inherited(state)

                    # testlib.pragma exempt:__hash__
                    inserted_objects.add((state, connection))

        if not postupdate:
            # call after_XXX extensions
            for state, connection, has_identity in tups:
                mapper = _state_mapper(state)
                if not has_identity:
                    if 'after_insert' in mapper.extension.methods:
                        mapper.extension.after_insert(mapper, connection, state.obj())
                else:
                    if 'after_update' in mapper.extension.methods:
                        mapper.extension.after_update(mapper, connection, state.obj())

    def __synchronize_inherited(self, state):
        sync.populate(state, self, state, self, self.__inherits_equated_pairs)

    def __postfetch(self, uowtransaction, connection, table, state, resultproxy, params, value_params):
        """After an ``INSERT`` or ``UPDATE``, assemble newly generated
        values on an instance.  For columns which are marked as being generated
        on the database side, set up a group-based "deferred" loader
        which will populate those attributes in one query when next accessed.
        """

        postfetch_cols = resultproxy.postfetch_cols()
        generated_cols = list(resultproxy.prefetch_cols())

        if self.polymorphic_on:
            po = table.corresponding_column(self.polymorphic_on)
            if po:
                generated_cols.append(po)
        if self.version_id_col:
            generated_cols.append(self.version_id_col)

        for c in generated_cols:
            if c.key in params:
                self._set_state_attr_by_column(state, c, params[c.key])

        deferred_props = [prop.key for prop in [self._columntoproperty[c] for c in postfetch_cols]]

        if deferred_props:
            if self.eager_defaults:
                _instance_key = self._identity_key_from_state(state)
                state.dict['_instance_key'] = _instance_key
                uowtransaction.session.query(self)._get(_instance_key, refresh_instance=state, only_load_props=deferred_props)
            else:
                _expire_state(state, deferred_props)

    def _delete_obj(self, states, uowtransaction):
        """Issue ``DELETE`` statements for a list of objects.

        This is called within the context of a UOWTransaction during a
        flush operation.
        """

        if self.__should_log_debug:
            self.__log_debug("_delete_obj() start")

        if 'connection_callable' in uowtransaction.mapper_flush_opts:
            connection_callable = uowtransaction.mapper_flush_opts['connection_callable']
            tups = [(state, connection_callable(self, state.obj())) for state in states]
        else:
            connection = uowtransaction.transaction.connection(self)
            tups = [(state, connection) for state in states]

        for (state, connection) in tups:
            mapper = _state_mapper(state)
            if 'before_delete' in mapper.extension.methods:
                mapper.extension.before_delete(mapper, connection, state.obj())

        deleted_objects = util.Set()
        table_to_mapper = {}
        for mapper in self.base_mapper.polymorphic_iterator():
            for t in mapper.tables:
                table_to_mapper[t] = mapper

        for table in sqlutil.sort_tables(table_to_mapper.keys(), reverse=True):
            delete = {}
            for (state, connection) in tups:
                mapper = _state_mapper(state)
                if table not in mapper._pks_by_table:
                    continue

                params = {}
                if not _state_has_identity(state):
                    continue
                else:
                    delete.setdefault(connection, []).append(params)
                for col in mapper._pks_by_table[table]:
                    params[col.key] = mapper._get_state_attr_by_column(state, col)
                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    params[mapper.version_id_col.key] = mapper._get_state_attr_by_column(state, mapper.version_id_col)
                # testlib.pragma exempt:__hash__
                deleted_objects.add((state, connection))
            for connection, del_objects in delete.iteritems():
                mapper = table_to_mapper[table]
                def comparator(a, b):
                    for col in mapper._pks_by_table[table]:
                        x = cmp(a[col.key],b[col.key])
                        if x != 0:
                            return x
                    return 0
                del_objects.sort(comparator)
                clause = sql.and_()
                for col in mapper._pks_by_table[table]:
                    clause.clauses.append(col == sql.bindparam(col.key, type_=col.type))
                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    clause.clauses.append(mapper.version_id_col == sql.bindparam(mapper.version_id_col.key, type_=mapper.version_id_col.type))
                statement = table.delete(clause)
                c = connection.execute(statement, del_objects)
                if c.supports_sane_multi_rowcount() and c.rowcount != len(del_objects):
                    raise exceptions.ConcurrentModificationError("Deleted rowcount %d does not match number of objects deleted %d" % (c.rowcount, len(del_objects)))

        for state, connection in deleted_objects:
            mapper = _state_mapper(state)
            if 'after_delete' in mapper.extension.methods:
                mapper.extension.after_delete(mapper, connection, state.obj())

    def _register_dependencies(self, uowcommit):
        """Register ``DependencyProcessor`` instances with a
        ``unitofwork.UOWTransaction``.

        This call `register_dependencies` on all attached
        ``MapperProperty`` instances.
        """

        for prop in self.__props.values():
            prop.register_dependencies(uowcommit)
        for dep in self._dependency_processors:
            dep.register_dependencies(uowcommit)

    def cascade_iterator(self, type_, state, halt_on=None):
        """Iterate each element and its mapper in an object graph,
        for all relations that meet the given cascade rule.

        type\_
          The name of the cascade rule (i.e. save-update, delete,
          etc.)

        state
          The lead InstanceState.  child items will be processed per
          the relations defined for this object's mapper.

        the return value are object instances; this provides a strong
        reference so that they don't fall out of scope immediately.
        """

        visited_instances = util.IdentitySet()
        visitables = [(self.__props.itervalues(), 'property', state)]

        while visitables:
            iterator,item_type,parent_state = visitables[-1]
            try:
                if item_type == 'property':
                    prop = iterator.next()
                    visitables.append((prop.cascade_iterator(type_, parent_state, visited_instances, halt_on), 'mapper', None))
                elif item_type == 'mapper':
                    instance, instance_mapper, corresponding_state  = iterator.next()
                    yield (instance, instance_mapper)
                    visitables.append((instance_mapper.__props.itervalues(), 'property', corresponding_state))
            except StopIteration:
                visitables.pop()

    def _instance(self, context, row, result=None, polymorphic_from=None, extension=None, only_load_props=None, refresh_instance=None):
        if not extension:
            extension = self.extension

        if 'translate_row' in extension.methods:
            ret = extension.translate_row(self, context, row)
            if ret is not EXT_CONTINUE:
                row = ret

        if polymorphic_from:
            # if we are called from a base mapper doing a polymorphic load, figure out what tables,
            # if any, will need to be "post-fetched" based on the tables present in the row,
            # or from the options set up on the query
            if ('polymorphic_fetch', self) not in context.attributes:
                if self in context.query._with_polymorphic:
                    context.attributes[('polymorphic_fetch', self)] = (polymorphic_from, [])
                else:
                    context.attributes[('polymorphic_fetch', self)] = (polymorphic_from, [t for t in self.tables if t not in polymorphic_from.tables])
                
        elif not refresh_instance and self.polymorphic_on:
            discriminator = row[self.polymorphic_on]
            if discriminator is not None:
                try:
                    mapper = self.polymorphic_map[discriminator]
                except KeyError:
                    raise exceptions.AssertionError("No such polymorphic_identity %r is defined" % discriminator)
                if mapper is not self:
                    return mapper._instance(context, row, result=result, polymorphic_from=self)

        # determine identity key
        if refresh_instance:
            try:
                identitykey = refresh_instance.dict['_instance_key']
            except KeyError:
                # super-rare condition; a refresh is being called
                # on a non-instance-key instance; this is meant to only
                # occur wihtin a flush()
                identitykey = self._identity_key_from_state(refresh_instance)
        else:
            identitykey = self.identity_key_from_row(row)
        
        session_identity_map = context.session.identity_map

        if identitykey in session_identity_map:
            instance = session_identity_map[identitykey]
            state = instance._state

            if self.__should_log_debug:
                self.__log_debug("_instance(): using existing instance %s identity %s" % (instance_str(instance), str(identitykey)))

            isnew = state.runid != context.runid
            currentload = not isnew

            if not currentload and context.version_check and self.version_id_col and self._get_attr_by_column(instance, self.version_id_col) != row[self.version_id_col]:
                raise exceptions.ConcurrentModificationError("Instance '%s' version of %s does not match %s" % (instance, self._get_attr_by_column(instance, self.version_id_col), row[self.version_id_col]))
        elif refresh_instance:
            # out of band refresh_instance detected (i.e. its not in the session.identity_map)
            # honor it anyway.  this can happen if a _get() occurs within save_obj(), such as
            # when eager_defaults is True.
            state = refresh_instance
            instance = state.obj()
            isnew = state.runid != context.runid
            currentload = True
        else:
            if self.__should_log_debug:
                self.__log_debug("_instance(): identity key %s not in session" % str(identitykey))

            if self.allow_null_pks:
                for x in identitykey[1]:
                    if x is not None:
                        break
                else:
                    return None
            else:
                if None in identitykey[1]:
                    return None
            isnew = True
            currentload = True

            if 'create_instance' in extension.methods:
                instance = extension.create_instance(self, context, row, self.class_)
                if instance is EXT_CONTINUE:
                    instance = attributes.new_instance(self.class_)
                else:
                    attributes.manage(instance)
            else:
                instance = attributes.new_instance(self.class_)

            if self.__should_log_debug:
                self.__log_debug("_instance(): created new instance %s identity %s" % (instance_str(instance), str(identitykey)))

            state = instance._state
            instance._entity_name = self.entity_name
            instance._instance_key = identitykey
            instance._sa_session_id = context.session.hash_key
            session_identity_map[identitykey] = instance

        if currentload or context.populate_existing or self.always_refresh:
            if isnew:
                state.runid = context.runid
                context.progress.add(state)

            if 'populate_instance' not in extension.methods or extension.populate_instance(self, context, row, instance, only_load_props=only_load_props, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE:
                self.populate_instance(context, instance, row, only_load_props=only_load_props, instancekey=identitykey, isnew=isnew)
        
        else:
            # populate attributes on non-loading instances which have been expired
            # TODO: also support deferred attributes here [ticket:870]
            if state.expired_attributes: 
                if state in context.partials:
                    isnew = False
                    attrs = context.partials[state]
                else:
                    isnew = True
                    attrs = state.expired_attributes.intersection(state.unmodified)
                    context.partials[state] = attrs  #<-- allow query.instances to commit the subset of attrs

                if 'populate_instance' not in extension.methods or extension.populate_instance(self, context, row, instance, only_load_props=attrs, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE:
                    self.populate_instance(context, instance, row, only_load_props=attrs, instancekey=identitykey, isnew=isnew)
            
        if result is not None and ('append_result' not in extension.methods or extension.append_result(self, context, row, instance, result, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE):
            result.append(instance)

        return instance

    def populate_instance(self, selectcontext, instance, row, ispostselect=None, isnew=False, only_load_props=None, **flags):
        """populate an instance from a result row."""

        snapshot = selectcontext.path + (self,)
        # retrieve a set of "row population" functions derived from the MapperProperties attached
        # to this Mapper.  These are keyed in the select context based primarily off the
        # "snapshot" of the stack, which represents a path from the lead mapper in the query to this one,
        # including relation() names.  the key also includes "self", and allows us to distinguish between
        # other mappers within our inheritance hierarchy
        (new_populators, existing_populators) = selectcontext.attributes.get(('populators', self, snapshot, ispostselect), (None, None))
        if new_populators is None:
            # no populators; therefore this is the first time we are receiving a row for
            # this result set.  issue create_row_processor() on all MapperProperty objects
            # and cache in the select context.
            new_populators = []
            existing_populators = []
            post_processors = []
            for prop in self.__props.values():
                (newpop, existingpop, post_proc) = selectcontext.exec_with_path(self, prop.key, prop.create_row_processor, selectcontext, self, row)
                if newpop:
                    new_populators.append((prop.key, newpop))
                if existingpop:
                    existing_populators.append((prop.key, existingpop))
                if post_proc:
                    post_processors.append(post_proc)

            # install a post processor for immediate post-load of joined-table inheriting mappers
            poly_select_loader = self._get_poly_select_loader(selectcontext, row)
            if poly_select_loader:
                post_processors.append(poly_select_loader)

            selectcontext.attributes[('populators', self, snapshot, ispostselect)] = (new_populators, existing_populators)
            selectcontext.attributes[('post_processors', self, ispostselect)] = post_processors

        if isnew or ispostselect:
            populators = new_populators
        else:
            populators = existing_populators

        if only_load_props:
            populators = [p for p in populators if p[0] in only_load_props]

        for (key, populator) in populators:
            selectcontext.exec_with_path(self, key, populator, instance, row, ispostselect=ispostselect, isnew=isnew, **flags)

        if self.non_primary:
            selectcontext.attributes[('populating_mapper', instance._state)] = self

    def _post_instance(self, selectcontext, state, **kwargs):
        post_processors = selectcontext.attributes[('post_processors', self, None)]
        for p in post_processors:
            p(state.obj(), **kwargs)

    def _get_poly_select_loader(self, selectcontext, row):
        """set up attribute loaders for 'select' and 'deferred' polymorphic loading.

        this loading uses a second SELECT statement to load additional tables,
        either immediately after loading the main table or via a deferred attribute trigger.
        """

        (hosted_mapper, needs_tables) = selectcontext.attributes.get(('polymorphic_fetch', self), (None, None))

        if hosted_mapper is None or not needs_tables:
            return

        cond, param_names = self._deferred_inheritance_condition(hosted_mapper, needs_tables)
        statement = sql.select(needs_tables, cond, use_labels=True)

        if hosted_mapper.polymorphic_fetch == 'select':
            def post_execute(instance, **flags):
                if self.__should_log_debug:
                    self.__log_debug("Post query loading instance " + instance_str(instance))

                identitykey = self.identity_key_from_instance(instance)
                
                only_load_props = flags.get('only_load_props', None)

                params = {}
                for c, bind in param_names:
                    params[bind] = self._get_attr_by_column(instance, c)
                row = selectcontext.session.connection(self).execute(statement, params).fetchone()
                self.populate_instance(selectcontext, instance, row, isnew=False, instancekey=identitykey, ispostselect=True, only_load_props=only_load_props)
            return post_execute
        elif hosted_mapper.polymorphic_fetch == 'deferred':
            from sqlalchemy.orm.strategies import DeferredColumnLoader

            def post_execute(instance, **flags):
                def create_statement(instance):
                    params = {}
                    for (c, bind) in param_names:
                        # use the "committed" (database) version to get query column values
                        params[bind] = self._get_committed_attr_by_column(instance, c)
                    return (statement, params)

                props = [prop for prop in [self._get_col_to_prop(col) for col in statement.inner_columns] if prop.key not in instance.__dict__]
                keys = [p.key for p in props]
                
                only_load_props = flags.get('only_load_props', None)
                if only_load_props:
                    keys = util.Set(keys).difference(only_load_props)
                    props = [p for p in props if p.key in only_load_props]
                    
                for prop in props:
                    strategy = prop._get_strategy(DeferredColumnLoader)
                    instance._state.set_callable(prop.key, strategy.setup_loader(instance, props=keys, create_statement=create_statement))
            return post_execute
        else:
            return None

    def _deferred_inheritance_condition(self, base_mapper, needs_tables):
        base_mapper = base_mapper.primary_mapper()

        def visit_binary(binary):
            leftcol = binary.left
            rightcol = binary.right

            if leftcol is None or rightcol is None:
                return
            if leftcol.table not in needs_tables:
                binary.left = sql.bindparam(None, None, type_=binary.right.type)
                param_names.append((leftcol, binary.left))
            elif rightcol.table not in needs_tables:
                binary.right = sql.bindparam(None, None, type_=binary.right.type)
                param_names.append((rightcol, binary.right))

        allconds = []
        param_names = []

        for mapper in self.iterate_to_root():
            if mapper is base_mapper:
                break
            if not mapper.single:
                allconds.append(visitors.traverse(mapper.inherit_condition, clone=True, visit_binary=visit_binary))
        
        return sql.and_(*allconds), param_names

Mapper.logger = logging.class_logger(Mapper)


object_session = None

def _load_scalar_attributes(instance, attribute_names):
    mapper = object_mapper(instance)
    global object_session
    if not object_session:
        from sqlalchemy.orm.session import object_session
    session = object_session(instance)
    if not session:
        try:
            session = mapper.get_session()
        except exceptions.InvalidRequestError:
            raise exceptions.UnboundExecutionError("Instance %s is not bound to a Session, and no contextual session is established; attribute refresh operation cannot proceed" % (instance.__class__))

    state = instance._state
    if '_instance_key' in state.dict:
        identity_key = state.dict['_instance_key']
        shouldraise = True
    else:
        # if instance is pending, a refresh operation may not complete (even if PK attributes are assigned)
        shouldraise = False
        identity_key = mapper._identity_key_from_state(state)

    if session.query(mapper)._get(identity_key, refresh_instance=state, only_load_props=attribute_names) is None and shouldraise:
        raise exceptions.InvalidRequestError("Could not refresh instance '%s'" % instance_str(instance))

